To get the No Mercy / ruthless ending in Roblox Undertale: The Obby , you first need to finish the True Ending, then fight 1 monster in each main area, and finally look for Chara in the Ruins after beating No Mercy. The game’s FAQ also says you must spare Papyrus, Undyne, and Alphys to unlock True Ending first.

Steps

  1. Complete a normal run to reach the Neutral Ending.
  1. Get the True Ending by sparing Papyrus, Undyne, and Alphys, then hanging out with them in their houses.
  1. After that, fight 1 monster per main area to trigger No Mercy.
  1. Beat No Mercy, then go to the Ruins to find Chara.

Important note

The game’s own FAQ says the No Mercy route is only available after True Ending, so you cannot skip straight to it.

Clean version

If by “ruthless ending” you meant the hardest or most aggressive route, this is the path the game describes as No Mercy.

TL;DR: Finish True Ending first, then fight one monster in each main area, then beat No Mercy and search the Ruins for Chara.